How to remove the upper tabs from the UI?(i.e Layout, Modeling, Sculpting etc.)
You could always just right-click on those tabs and delete, with the possibility of deleting all of them except one: 
It's possible to rename them by double clicking on the text.
Alternatively, you can take lines 45 through 56 of the space_topbar.py file and comment them out:

Just a side note: The space_topbar.py file can be easily found by right clicking any of the top tabs and clicking &quot;Edit Source&quot;, which will populate the file inside the script editor (via the file dropdown)